1. Field of the Invention:
The present invention relates to a sewing machine capable of adjusting a feed pitch or stitch length in a work piece, and more particularly to a sewing machine capable of setting the feed pitch or stitch length of a first stitch to zero in the work piece at the beginning of a sewing operation.
2. Description of the Prior Art:
A conventional sewing machine is constructed of: a sewing needle which is reciprocable in a vertical direction and swingable in a lateral direction, when the needle is above a work piece to be sewn; a thread to form stitches; feed means which cooperates with a presser foot in synchronism with the needle to feed the work piece through a so-called parallelogramic four-step motion; and driving means for driving these components of the sewing machine. The work feed means includes a feed dog for feeding the work with respect to the needle when the feed dog is disposed above a throat plate which supports the work piece while the fabric or work is pressed against the throat plate by a vertically reciprocable presser foot.
As is apparent from the above, the needle is disposed in a position above the throat plate when the feed dog is moved upward from the throat plate, so that, the feed pitch or stitch length is regulated while the needle is disposed in a position below the throat plate to enable the needle-thread catching means to catch the needle thread to form a stitch. After completion of regulation of the feed pitch or stitch length, the needle moves upward and the feed dog moves upward from the throat plate to feed the work piece at a rate of the regulated feed pitch or stitch length.
Horizontal feed of the work piece conducted by the feed dog continues until the needle is moved halfway down to the throat plate or the work from a subsequent stitch.
Namely, the feed dog or the feed means is so constructed as to make substantially a half of a total work feed stroke when the needle is positioned in the vicinity of an upper dead point of the needle, in which position the needle may be laterally swingable and the remaining half of the stroke of the feed dog continues to feed the work until the needle moves down half way to the work piece.
The conventional sewing machine having the above construction has a problem in that: in case a plurality of small constituent patterns are optionally combined to form a large-sized pattern, it is impossible to correctly determine a needle position for the first stitch of the subsequent pattern after completion of a sewing operation of a first one of the constituent patterns, since, as mentioned above, the feed dog of the feed means continues to make the remaining half of its work feed stroke of the last stitch of the precededly sewn pattern while the needle comes down to the work.
In order to resolve the above problem, another conventional sewing machine, for example such as one proposed in Japanese Patent Laid-Open Nos. 61-279284 and 61-272083 is provided with a means for setting a feed pitch of the last stitch on zero at the end of a sewing operation of one of the constituent patterns to enable the sewing needle to begin to stitch the work piece at the desired point of the work piece in the subsequent sewing operation of a next one of the constituent patterns.
However, in general, in sewing operation, not only the constituent patterns but also continuous straight stitch, zigzag stitch as shown in FIG. 10 (a) and like stitches are frequently employed in the sewing machine.
In addition, in sewing operation of the large-sized pattern, it is often required to stop the sewing operation of one of the constituent patterns before completion of such sewing operation.
For example, in case that a first sewing operation of a zigzag stitch or pattern having a stitch length "c" and stitch width "W" is stopped at a point "a" as shown in FIG. 10 (b), a subsequent sewing operation of the same zigzag stitch starts at a point "b1" spaced apart from the point "b" as shown in FIG. 10 (b), because the stitch length is automatically set on zero at the end of the first sewing operation to cause a first stitch of the subsequent sewing operation to have no stitch length.
Then, the stitch length "c" of the pattern is set when the sewing needle point is disposed in a position below the throat plate to make it possible that a second stitch of the subsequent sewing operation has a stitch length "c". Consequently, in the conventional sewing machine, in case that the sewing operation of a pattern is temporarily stopped, it is impossible to start a sewing operation forming the pattern in continuous manner.